Saw-tooth wave generator



June 29, 1948. H. BRANSON SAWTOOTH WAVE GENERATOR 2 Sheets-Sheet 1 Filed Sept. 2'7, 1944 FIG. 1

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Filed Sept. 2'7, 1944 H. BRANSON SAWTOOTH WAVE GENERATOR 2 Sheets-Shet 2 INVENTOR.

Brans 0 27 Patented June 29, 1948 SAW-TOOTH WAVE GENERATOR Harry Branson, Hightstown, N. 1., assignor, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application September 27, 1944, Serial No. 556,049

12 Claims.

This invention relates to capacitor discharge circuits such, for example, as are used in defleeting signal generators for cathode ray tubes.

More particularly, this invention relates to capacitor discharge circuits for use in deflecting signal generators to effect radial or polar scanning of cathode ray tubes.

When generating deflecting signals, for example in the generation of saw-tooth wave shape voltages, it is common practice to utilize the low impedance of a conducting space discharge device, such as an arc tube or a multi-electrode vacuum tube. for the discharge path of a charged condenser. The multielectrode vacuum tube is, of course, preferred for the higher frequency sawtooth wave generators. Since. in conventional capacitor discharge circuits employing space discharge devices the conduction current of the tube flows in one direction only, a charged capacitor may be discharged only when the charge on the capacitor is of the correct polarity, Which polarity is such that the capacitor terminal connected to the anode of the tube is charged to a positive potential in order that the charge on the condenser may flow through the internal impedance of the tube when the tube is conducting. A capacitor which may be charged either positively or negatively would then require at least two tubes to effect discharge for either polarity of charge on the capacitor.

It is, therefore, an obiect of the present invention to provide a simple and novel means for discharging a positively or negatively charged capacitor.

It is also an object of the present invention to provide a novel means for generating deflecting signals of either positive or negative polarity.

Another object of the present invention is to provide a simple novel system to generate deflecting signals to effect radial scanning of a cathode ray tube.

It is furthermore an object of the invention to provide methods and apparatus for controlling flow of current in either direction through a circuit by means of a single control unit.

Other objects and advantages of this invention will become apparent during the course of the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 shows schematically the preferred embodiment of the present invention;

Fig. 2 is a typical characteristic curve of a space discharge device employed in invention;

the present v Fig. 3 represents one form of voltage output obtainable from the invention; and

Fig. 4 is a block diagram of one arrangement of equipment to produce the necessary deflecting voltages for radial scanning of a cathode ray tube.

Referring to Fig. 1, there is schematically shown a current controlling device such as a four electrode or tetrode type vacum tube T, having a control element or control grid H, which is preferably biased to cut-off by a suitable bias voltage from a source C applied through a grid resistor i2. A second grid l3, which may be referred to as a collector anode, is operated at a suitable positive potential as indicated by its direct connection to the anode voltage supply B. The plate I4, which may be referred to as the target, obtains its potential from anode voltage supply B" by way of the conductor 2|, terminal a, source of voltage V, terminal I; resistor l5, and conductor 20. Energy storage means such as a capacitor I5 is connected between-the plate or target M and the terminal a. The output voltage of the capacitor discharge circuit is obtained across condenser l6 as indicated by output terminals l1 and I8. An input terminal for a positive triggering pulse is shown at IS.

A signal source for supplying such a trigger pulse is schematically represented by a rectangle S.

The resistance-capacitance combination of 15 and I6 forms a conventional charging circuit, with the capacitor or condenser l6 being slowly charged by voltage V through resistance It. The portion of the circuit to the left of the vertical dot dash line a::r will be recognized as the rapid discharge path for condenser it. When the upper terminal of condenser I6 is charged to a positive potential by voltage V and a positive pulse of sufiicient magnitude to permit tube T to conduct is applied to the input terminal is, the condenser I6 will, of course, be discharged through the ,path containing the plate conductor 20 and the plate return conductor 21 in a manner similar to conventional space discharge circuits. However, with conventional circuits employing space discharge tubes as the discharge resistance, the condenser 18 would not be discharged when its upper terminal was charged to a negative potential by voltage source V. The discharge of condenser l6, when its upper terminal is charged to a negative potential, is accomplished in the present invention with the single tube T by employing a tube in which the efiects of secondary emission are sufiicient to produce a negative plate or target current when certain relations are established between the electrode potentials. For example, a vacuum tube with characteristics similar to the RCA tetrode UY224 as given in Fig. 327, page 600, of Dr. E. L. Chaffees book, Theory of Thermionic Vacuum Tubes, published in 1933 by McGraw-I-Iill Book Co., will, when operated with suitable electrode potentials, produce the required bilaterally conducting eifect to provide for the discharge of condenser it when charged to either a positive or negative polarity. In order to illustrate the desired result, that is, negative plate current for certain electrode potentials and positive plate current for certain other electrode potentials, produced by the secondary emission characteristic of a tetrode, one plate current-plate voltage curve for the UY224 tetrode is reproduced in Fig. 2. It is preferable that the operating potentials for tube T of Fig. 1 be chosen that the tube operates on the steepest characteristic curve. Thus the curve in Fig. 2 has been taken from the family of curves for the UY224 given in Fig. 327 of the above-mentioned book for a control grid potential of zero volts. Referring to Fig. 2 it will be noticed that over the portion of the characteristic curve bebetween the vertical reference lines u-w the relation between plate current and plate voltage is practically linear, and that also between the reference lines u-v the plate current is negative. The curve in Fig. 2 then shows that for certain plate potentials the plate current flows in one direction while for certain other plate potentials the direction of plate current flow is in the opposite direction. A capacitor placed in the plate circuit of a tube having similar characteristics may then be discharged for either polarity of charge on the capacitor.

The operation of the capacitor discharge circuit of the present invention will now be described with reference to Fig. 1 in which the tube T, for illustrative purposes only, is assumed to have the characteristics as given by the curve in Fig. 2.

The operating potentials of the tube T are so chosen that with no signal input to the terminal 09 the control grid H of tube T is biased to or beyond plate current cut-01f. For a signal input at terminal IQ of such magnitude as to permit tube '1' to operate on the proper portion of the desired characteristic curve as previously mentioned, the operating potentials for the second grid or collector anode I4 and for the plate or target l4 would be so chosen that with zero voltage between terminals a-b the plate current would be zero. For example, assuming tube T to have characteristics similar to those shown in Fig. 2, the signal voltage supplied by the trigger source S would preferably be of such magnitude to place control grid l l at zero bias. With the second grid 13 operating at a potential of 90 volts the voltage of anode supply B" would be approximately 66 volts as indicated at the vertical line '12. Preferably the signal source S is arranged to provide a substantially rectangular pulse wave of the desired amplitude. However, precise maintenance of a constant voltage signal is not a prerequisite to operability of the apparatus, since tubes such as the UY224, for example, exhibit the characteristic of negative plate current with negative grid potential also, although to a diminished degree. The preferred grid potential will obviously depend upon the type of tube employed.

With no input signal, the condenser [6 would be charged by voltage source V in a normal manner. A positive input pulse will permit tube T to discharge condenser l6 whether this condenser is charged to a positive or negative polarity by the voltage source V, within, of course, certain voltage limitations. This is evident from the characteristic curve in Fig. 2 which indicates a positive current flow in the plate circuit of tube T for a positive charge on the upper terminal of condenser I6 (which charge raises the potential on the plate M of tube T above the operating potential of 66 volts shown at line 1; in Fig. 2), and negative current flow in the plate circuit of tube T for a negative charge on the upper terminal of condenser I 6 (which negative charge lowers the potential on the plate M below the operating potential of 66 volts).

Thus saw tooth wave shape voltages of either polarity may be generated across condenser it by the capacitor discharge circuit of this invention. The frequency of the saw tooth voltage will, of course, depend upon the frequency of the input pulses, and the linearity of the wave front of the saw tooth voltage will be governed by the relation between the voltage of source V and the voltage to which condenser I6 is permitted to charge, which factors are well known in the art.

Now if the voltage from source V in Fig. 1 is a sine wave alternating voltage and the operating conditions of the capacitor discharge circuit represented by the elements to the left of line :rx in Fig. l are properly chosen, there may be developed across condenser IS a series of saw-tooth voltages the envelope of which will be a sine wave. Such a series of saw-tooth voltage are illustrated in. Fig. 3. Referring to Fig. 3, the dashed line sine wave represents the wave form of the voltage from source V of Fig. 1, and the solid line saw tooth wave shapes represent the output voltage at terminals I! and 18 of Fig. 1. For the sake of clarity only a few saw-tooth voltage waves for one cycle of sine wave voltage from source V have been assumed and shown in Fig. 3, and the amplitudes of the saw-tooth voltages have been shown in greater proportion to the amplitudes of the sine wave voltage than would be found in actual practice. To obtain a series of linear saw-tooth voltages whose envelope is a sine wave the operating conditions for the capacitor discharge circuit should preferably be such that tube T operates on that portion of its characteristic curve similar to that part of the curve in Fig. 2 between the vertical lines u-w in order that tube T when conducting will appear as a pure resistance of constant value between conductors 20 and 2| of Fig. 1 within the range of voltages to which capacitor is may be charged. Also it is preferable for the sake of linearity of the saw-tooth wave that the frequency of the input pulses be much higher than the frequency of the sine wave voltage from source V and that the voltage to which condenser [E is permitted to charge be but a small portion of the voltage appearing at terminals a-b from source V. The generation of the form of output voltagepictured in Fig. 3 is, of course, due to the constantly changing amplitude of the voltage of source V and consequently the constantly changing voltage to which condenser 16 is charged after each discharge.

By applying saw-tooth voltages of the form shown in Fig. 3 to one pair of deflecting plates of a cathode ray tube and similar saw-tooth voltages, whose envelope is displaced degrees from the envelope of the above saw-tooth voltages, to the other pair of deflecting plates the cathode ray tube would be supplied with the necessary defleeting signals to provide for the radial or polar scanning of the cathode ray tube screen. The electron beam of the cathode ray tube would then be deflected from the center of the screen radially outward in a series of straight lines. The number of scanning lines would depend upon the number of positive input pulses for each cycle of sine wave voltage from source V of .Fig. 1 and the angular velocity of the radial scanning line would depend upon the frequency of the sine wave voltage from source V.

A suggested system for generating the necessary deflecting voltages to effect radial scanning of a cathode ray tube is given in block diagram form in Fig. 4. Referring to Fig. 4, a source of sine wave voltage 30 applies a sine wave voltage simultaneously to two phase shifting networks 3! and 32. These networks are so arranged that the voltage output of network 3i is 90 degrees out of phase with the output voltage of network 32. The sine wave output voltage of one phase shifting network, for example, network 3!, is applied to the terminals Ur-b of one capacitor discharge circuit, similar to that shown in Fig. 1, indicated at I in Fig. 4, and the sine wave output voltage of the other phase shifting network 32 is applied to the terminals a--b of another similar capacitor discharge circuit, represented at l l in Fig. 4. The saw-tooth voltage output from I is applied to one pair of deflecting plates and the saw-tooth output of II is applied to the other pair of deflecting plates. It is, of course, understood that the saw-tooth voltages from I and II may be amplified if necessary by conventional deflection signal amplifiers.

In Fig, 4 the saw-tooth voltages from capacitor discharge circuit I are shown applied to the vertical deflecting plates V-V, while the saw-tooth voltages from II, having an envelope which is 90 degrees out of phase with the envelope of the saw-tooth voltages from I, are shown applied to the horizontal deflecting plates I-II-I. The resultant electrostatic field set up by these volt ages. on the deflecting plates causes the electron beam of the cathode ray tube to produce a pat" tern on the fluorescent screen similar to that shown at P in Fig. 4. As previously stated, the number of lines in the scanning pattern depends upon the number of positive input pulses per cycle of sine wave voltage. The pattern on the cathode ray tube screen may be either a series of lines extending radially outward from the center, such as indicated at P in Fig. 4, or the pattern may be one line extending from the center and rotating about the center of the screen in successive angular positions depending upon the persistence of the fluorescent screen and upon the frequency of the sine wave voltage and whether means are provided for interrupting the beam of the cathode ray tube synchronously with the saw-tooth wave.

While this invention has been described and illustrated in Figs. 3 and 4 for the generation of saw-tooth wave shape voltages suitable for deflecting the electron beam of the cathode ray tube by electrostatic means, it will be apparent to those skilled in the art that suitable wave shape voltages for deflecting the electron beam by magnetic deflecting means may be generated by the circuit of this invention.

Although this invention has been described with particular reference to the drawings, it will be understood that the invention is capable of various forms of physical expression, and is to 6 be limited only by the scope or the appended claims. i

I claim:

1. A sweep circuit for apolar-scan oscilloscope comprising in combination a pair of condenser discharge circuits, each for energizing one of two difierent transverse deflection circuits of a cathode ray tube, each such condenser discharge circuit includin a vacuum tube biased for control of discharge current in either direction, sine wave means for energizing said discharge circuits, and tripping means of considerably greater frequency than the sine wave meansfor tripping the discharge circuits.

2. A polar-scan oscilloscope comprising in combination, a cathode ray tube with transverse deflection circuits, a pair of condenser discharge circuits each including a vacuum tube biased for control of discharge current in either direction, each deflection circuit being connected to one of said condenser discharge circuits, sine wave means for energizing said discharge circuits, and tripping means of considerably greater frequency than the sine wave means for tripping the discharge circuits.

3. A polar-scan indicator comprising an indicating device with transverse deflecting means, a pair of condenser discharge circuits coupled to said deflecting means for actuating the same, such discharge circuits, each including a control element biased for control of current in either direction, alternating-current means for energizing the discharge circuits and tripping means for the discharge circuits.

4. An indicator having transverse deflecting means, energy storage means coupled to said de fleeting means for actuating the same, a bilaterally conducting current control device connected to said energy storage means, alternating-current means for supplying the energy storage means, and means for tripping the current control device.

5. In combination, a discharge device including cathode and plate electrodes and operable over a plate current-plate voltage characteristic which extends on opposite sides of the zero plate current axis, a condenser connected across said discharge device, means for normally maintaining the plate voltage of said device at a value corresponding to the intersection of the plate current-plate voltage characteristic with the zero plate current axis, and means for controlling the flow of current from said condenser through said discharge device, whereby said condenser is discharged in either direction whenever its potential difference is raised by an external source of either polarity.

6. In a system for discharging an energy storage device in which the energy is at times of positive polarity and at other times of negative polarity, the method of discharging said device through a vacuum tube having a collector anode and a target or plate, which method comprises the steps of biasing the collector anode to a value producing a plate current-plate voltage characteristic curve having a region of negative plate current in a positive slope portion of the curve crossing the zero plate current axis, normally maintaining the plate voltage at a value substantially equalling that at which said positive slope portion intersects the zero plate current axis, and controlling the flow of current from said storage device through said tube, whereby to discharge said storage device regardless of the polarity of the energy stored therein.

7. The method of alternately charging an energy storage device with energy of positive and negative polarity and discharging said device through a vacuum tube havinga control grid, a collector anode and a target or plate connected to said device, which method comprises the steps of normally biasing said control grid negatively to a cut-off value, biasing said collector anode to a value which with a predetermined control grid potential produces 'a plate current-plate voltage characterlsticcurve having a region of negative plate current in a positive slope portion crossing the zero "plate current axis, normally maintain the plate voltage at a value substantially equalling that at which the characteristic curve intercepts the zero plate current axis, charging said storage device alternately to a positive and negative polarity, and raising the control grid to said predetermined potential when the tube is to be rendered conductive for discharging said storage device.

8. In combination, a condenser, :a discharge device connected thereto and a source of anode voltage connected in series with the discharge device and the condenser, said discharge device 1 having a target, a collector anode and a control grid with means for producing such potentials of the control grid and the collector anodeas to cause operation of the .tube over a positive slope'portion of the plate current-plate voltage characteristic curve crossing the zero plate current axis, said source of anode voltage having such a magnitude as to correspond to the point of Zero plate current in the characteristic curve of the tube, whereby externally produced difference in potential across the condenser results in discharge thereof "in either direction through the discharge device, dependent upon the polarity of the potentialdifference across the condenser.

9. Apparatus as in claim 5, wherein an alternating current source is connected to the condenser for charging it, the discharge device is provided with a control grid normally biased to-cut' oii'a tripping source of'greater frequency than the alternating current source is connected to said control grid for intermittently renderin the discharge device conducting during each cycle 'of the alternating current source.

10. A bilateralrcondenserdischarge device comprising an electronic discharge tube, said tube including a plate or :targetelectrode, a collector anode and a control grid, and having suificient secondary emission efiect to 'produce negative current flow through said target with predetermined values of control grid and. collector anode bias, means for bringing the control grid potential and the collector anode potential to the predetermined bias values at which negative target current may take place, and means for normally maintaining the target at a potential corresponding to that value above and below which target current fiows in a direction to discharge the condenser.

11. Apparatus as in claim 10, including means for normally biasing the control grid to cutofi, and a trigger source for raising the control grid potential to a sufficient value to produce conductive condition of the tube.

12. In combination, a condenser, a discharge device connected thereto and a source of anode voltage connected in series with the discharge device and the condenser, said discharge device having a target, a collector anode and a control grid with means for producing such potentials of the control grid and the collector anode as to cause operation of the tube in the portion of the plate current-plate voltage characteristic curve crossing the zero plate current axis, said source of anode voltage having such a magnitude as to correspond to the point or" zero plate current in the characteristic curve of the tube, whereby externally produced difference in potential across the condenser results in discharge thereof in either direction through the discharge device, dependent upon the polarity of the potential difierence across the condenser.

HARRY BRANSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

